We start with an 8" astronomical mirror - figured to within 1/8th wave surface accuracy:

A. Wavelength of green light: 550NM (0.00000055 Meters)B. Convert this to inches (x's 39.37): 0.00002165"C. 1/8th of the above would be 0.0000027"

So - just how smoooooth is 2.7 millionths of an Inch?

If we were to expand the diameter of our 8" mirror to One Mile - its (6 to 1 ratio) edge would stand almost 300 yards tall - and its finished face would have a surface accuracy of approximately 1/50th of an inch.

No matter how large the mirror, the surface accuracy must still be to within the same fraction of a wavelength of the part of the electromagnetic spectrum observed. A 3", 300", or 30,000" mirror for visual spectrum work would all need to be figured to the same 1/4 wavefront error.

The allowable error does not scale up with the aperture. If it did, big mirrors would be easier to figure than small ones (discounting the handling issues.)

I'm simply asking: Is a fiftieth of an inch surface error (for a mirror with a diameter of 63,360 inches) - the scaled-up equivalent for another - accurate to an eighth of the wavelength of green light, and having an 8 inch diameter?

I'm simply asking: Is a fiftieth of an inch surface error (for a mirror with a diameter of 63,360 inches) - the scaled-up equivalent for another - accurate to an eighth of the wavelength of green light, and having an 8 inch diameter?

I once saw a similar comparison. As I recall, it went like this:

If the Hale 200 inch at Palomar were scaled up so that it covered the surface of the United states, the bump would be about 4 inches.